1. Field of the Invention
This invention relates to a hydraulic tilt system for a marine propulsion, and more particularly to an improved hydraulic tilt system that provides a reliable tilting and holding operations of the marine propulsion.
2. Description of Related Art
A drive unit of an outboard motor is typically mounted on a transom of an associated watercraft by means of a bracket assembly which comprises a swivel bracket and a clamping bracket. The swivel bracket supports the drive unit for pivotal movement about a generally vertically extending axis. The clamping bracket is affixed to the transom of the associated watercraft and supports the swivel bracket for pivotal movement about a generally horizontally extending axis.
Usually, a hydraulic cylinder assembly is interposed between the swivel and clamping brackets to tilt up or down the drive unit. The cylinder assembly comprises a cylinder housing, a tilt piston slidably supported within the cylinder housing and defining a couple of fluid chambers. A piston rod is affixed to the tilt piston and extends therefrom through one of the fluid chambers. The cylinder housing is affixed to one of the swivel bracket and clamping bracket, while an outer end of the piston rod is affixed to the reminder of the brackets. A pressurizing mechanism including, for example, a fluid pump pressurizes fluid in the fluid chambers for causing reciprocal movement of the tilt piston within the cylinder housing so that the drive unit is tilted up or down. The hydraulic cylinder assembly and the pressurizing mechanism generally define a hydraulic tilt system.
Although various arrangements are applicable for the hydraulic tilt system, a shuttle valve assembly is one typical component that is employed in these arrangements. The shuttle valve assembly includes a shuttle cylinder housing having openings at both outer ends and a shuttle piston slidably supported within the shuttle cylinder housing. The openings are joined with each one of the fluid chambers in the cylinder housing. A pair of closure valves are provided for closing the openings of the outer ends of the cylinder housing. The shuttle piston defines a pair of shuttle chambers in the housing and has projections provided at both sides to confront the closure valves. A reversible fluid pump, for example, is joined to the shuttle chambers with its inlet-outlet ports. When one of the shuttle chambers is pressurized by the fluid pump, the closure valve at this shuttle valve is pushed out to permit fluid flow through the opening to the fluid chamber in the cylinder housing for effecting the tilt piston moves. Simultaneously, the shuttle valve moves toward the other closure valve and pushes the valve outwardly by its projection. Accordingly, the fluid in the other fluid chamber may return to the other inlet-outlet port through the opening at this side of the shuttle cylinder not to resist the movement of the tilt piston. A typical shuttle valve assembly is disclosed in U.S. Pat. No. 4,557,696.
The shuttle valve assembly is advantageous because the hydraulic tilt system can be neatly formed. However, a space for the hydraulic tilt system, which is defined in the bracket assembly and specifically between the swivel bracket and clamping bracket, is extremely narrow. In order to place the shuttle valve assembly in this space, improved shuttle valve assemblies are desirable.